A liquid crystal display or electrochromic display as a two-dimensional display device is composed of display elements (pixels) arranged in a two-dimensional array. A display brightness of each display element or the like is controlled by either of the so-called passive matrix method and active matrix method, and the active matrix method is superior in quality of image such as contrast of a displayed image and is the mainstream for large-screen and high-definition two-dimensional display devices.
In the active matrix method, it is necessary to form a control element such as a thin film transistor or thin film diode for each display element in order to control the display brightness or the like. Information such as brightnesses to be displayed in respective pixels is transmitted through one of signal lines routed in parallel with one direction of the two-dimensional array of the display elements, to the aforementioned control elements corresponding to the respective pixels, and further transmitted to one of the pixels.
In the case of the thin film transistors being used, a plurality of select lines are also formed in a direction approximately perpendicular to the signal lines. Each thin film transistors is located near one of intersections between the signal lines and the select lines, and each display element is also located near the thin film transistor, i.e., near an intersection between the signal line and the select line.
For one of the signal lines, a number of display elements are arranged along it via the thin film transistors (control elements). On the other hand, each control element is controlled in electrical continuity or electrical non-continuity by a select line arranged perpendicular to the signal lines and, by virtue of action of the select line and control element, an electric signal on a signal line at a certain time is transmitted to only one display element.
By sequentially changing the signal line to be selected at predetermined intervals of time and changing the display information such as the brightness on each signal line in synchronism therewith, it becomes feasible to display each of the two-dimensionally arrayed display elements sequentially at a predetermined brightness. On the other hand, each of the control elements not selected by a select line is in electrical non-continuity to maintain an electric signal accumulated in the display element and thus maintain the display in the predetermined brightness state.
The thin film transistors as the control elements described above are those fabricated as follows: a thin film of amorphous silicon or poly (polycrystalline) silicon is deposited on a substrate forming the display elements, and processed in part into thin film transistors.
There are also proposals on an attempt to fabricate the control elements, using semiconductor materials of predetermined rod-like single crystals or the like preliminarily formed, instead of using the semiconductor material of silicon or the like deposited on the substrate as in the prior art. This is a method of arranging the rod-like semiconductor materials on the display device in a manufacturing process, processing them into transistors, and thereby making them function as the control elements.
The method of forming the thin film of polysilicon or amorphous silicon on the substrate and processing it in part into the thin film transistors to form the active matrix display device as described above requires a thermal process in the step of depositing polysilicon or amorphous silicon, and substrate materials that can be used for the display device were limited to those with relatively high heat resistance.
Concerning the substrates for the display device, at least a substrate used on the front side needs to be transparent. Therefore, the substrate has to be transparent and have appropriate heat resistance, and therefore it was often the case that an expensive glass substrate was used.
Incidentally, in the method using the aforementioned rod-like semiconductor materials recently proposed, there is no need for directly forming the thin film of polysilicon or amorphous silicon on the semiconductor substrate, which drastically ease the requirement of heat resistance for the substrate. However, it is difficult to accurately locate the fine rod-like semiconductor materials at their respective predetermined locations among a lot of display elements.
It is then also contemplated to adopt a method of randomly scattering a number of rod-like semiconductor materials or the like formed separately, on a substrate in which a number of display pixels or pixel electrodes for display pixels, and signal lines are formed, and processing only the rod-like semiconductor materials accidentally arranged at desired locations, so as to function as transistors or the like, thereby to form the control elements. This method can form the high-quality semiconductor materials on the substrate without need for the substrate to pass through a high-temperature process and can also lead to reduction of cost of the substrate and the whole manufacturing process.
In this case, however, the rod-like semiconductor materials or the like not located at desired positions could cause electrical continuity (short circuit) between some essentially not to be brought into electrical continuity out of the plurality of signal lines and the plurality of pixel electrodes formed on the substrate, and there is thus a problem that it is difficult to manufacture a display device without any pixel defects.